[PATCH] nvme-tcp: Use __dev_get_by_name instead dev_get_by_name for OPT_HOST_IFACE

[Sagi Grimberg]

>> dev_get_by_name() finds network device by name but it also increases
>> reference count.
>> Increasing the ref count,
>> If nvme-tcp queue is present and the network device driver is removed
>> before nvme_tcp, we will face the following continuous log:
>>    "kernel:unregister_netdevice: waiting for <eth> to become
>>    free. Usage count = 2"
>> And rmmod further halts. Similar case arises during reboot/shutdown
>> with nvme-tcp queue present and both never completes.
>>
>> As a fix we will use __dev_get_by_name() which find network device by
>> name without increasing any reference counter.
> 
> And when you remove it without the refcount we'll now have a stale
> kernel pointer?

The netdev is not actually needed, its to make sure that it exist as
reference in the host_iface afaict (the netdev is never referenced
afterwards), and I'm pretty sure there was a matching put somewhere in
the former versions of this patch.